Two-dimensional endfire array with increased gain and side lobe reduction

Endfire arrays such as Yagi antennas can be analyzed in terms of the phase and amplitude distribution in a "virtual aperture" plane transverse to the axis of the array. A method for controlling the amplitude and phase across the virtual aperture is given. It is shown, in particular, that the virtual aperture area can be increased through the use of parasitic side arrays, and that at the same time control of the illumination function can be retained. Thus, it is possible to increase gain and reduce side lobes simultaneously without supergaining. Measured patterns are shown for three different array types. Type I is a Yagi antenna 6 wavelengths long, tuned for maximum gain by using a modified Hansen-Woodyard condition reported elsewhere. Types II and III are two-dimensional endfire arrays, also 6 wavelengths long. Type II was tuned for very low side lobe level (30 db), and Type III for maximum gain obtainable with a more moderate side lobe level (17 db). The gain of Type II was 30% above that of Type I, while the gain of Type III was 60% above Type I. The method presented demonstrates that controlled excitation of a two-dimensional parasitic array with a single feed (rather than a line source) is feasible.